1. Field of the Invention
This invention relates in general to a Physical Layer Device, and more particularly to a Physical Layer Device having power savings features operable during auto-negotiation for multiple technologies.
2. Description of Related Art
Recent advancements in the art of data communications have provided great strides in resource sharing amongst computer systems through the use of networks which offer reliable high-speed data channels. Networks allow versatility by defining a common standard for communication so that information according to a standard protocol may be exchanged across user applications. As the popularity of networks increase so does the demand for performance. More sophisticated protocols are being established to meet this demand and are utilizing existing twisted pair wires, as well as more advanced transmission media, in office buildings so that many users have access to shared resources at minimal expense.
As will be appreciated by those skilled in the art, communication networks and their operations can be described according to the Open Systems Interconnection (OSI) model which includes seven layers including an application, presentation, session, transport, network, link, and physical layer. The OSI model was developed by the International Organization for Standardization (ISO) and is described in "The Basics Book of OSI and Network Management" by Motorola Codex from Addison-Wesley Publishing Company, Inc., 1993 (First Printing September 1992), and which is incorporated by reference herein.
Each layer of the OSI model performs a specific data communications task, a service to and for the layer that precedes it (e.g., the network layer provides a service for the transport layer). The process can be likened to placing a letter in a series of envelopes before it is sent through the postal system. Each succeeding envelope adds another layer of processing or overhead information necessary to process the transaction. Together, all the envelopes help make sure the letter gets to the right address and that the message received is identical to the message sent. Once the entire package is received at its destination, the envelopes are opened one by one until the letter itself emerges exactly as written.
In a data communication transaction, however, each end user is unaware of the envelopes, which perform their functions transparently. For example, an automatic bank teller transaction can be tracked through the multi-layer OSI system. One multiple layer system (Open System A) provides an application layer that is an interface to a person attempting a transaction, while the other multiple layer system (Open System B) provides an application layer that interfaces with applications software in a bank's host computer. The corresponding layers in Open Systems A and B are called peer layers and communicate through peer protocols. These peer protocols provide communication support for a user's application, performing transaction related tasks such as debiting an account, dispensing currency, or crediting an account.
Actual data flow between the two open systems (Open System A and Open System B), however, is from top to bottom in one open system (Open System A, the source), across the communications line, and then from bottom to top in the other open system (Open System B, the destination). Each time that user application data passes downward from one layer to the next layer in the same system more processing information is added. When that information is removed and processed by the peer layer in the other system, it causes various tasks (error correction, flow control, etc.) to be performed.
The ISO has specifically defined all seven layers, which are summarized below in the order in which the data actually flows as they leave the source:
Layer 7, the application layer, provides for a user application (such as getting money from an automatic bank teller machine) to interface with the OSI application layer. That OSI application layer has a corresponding peer layer in the other open system, the bank's host computer.
Layer 6, the presentation layer, makes sure the user information (a request for $50 in cash to be debited from your checking account) is in a format (i.e., syntax or sequence of ones and zeros) the destination open system can understand.
Layer 5, the session layer, provides synchronization control of data between the open systems (i.e., makes sure the bit configurations that pass through layer 5 at the source are the same as those that pass through layer 5 at the destination).
Layer 4, the transport layer, ensures that an end-to-end connection has been established between the two open systems and is often reliable (i.e., layer 4 at the destination confirms the request for a connection, so to speak, that it has received from layer 4 at the source).
Layer 3, the network layer, provides routing and relaying of data through the network (among other things, at layer 3 on the outbound side an address gets placed on the envelope which is then read by layer 3 at the destination).
Layer 2, the data link layer, includes flow control of data as messages pass down through this layer in one open system and up through the peer layer in the other open system.
Layer 1, the physical interface layer, includes the ways in which data communications equipment is connected mechanically and electrically, and the means by which the data moves across those physical connections from layer 1 at the source to layer 1 at the destination.
The primary standard for Local and Metropolitan Area Network technologies is governed by IEEE Std. 802, which is incorporated by reference herein. IEEE Std. 802 describes the relationship among the family of 802 standards and their relationship to the ISO OSI Basic Reference Model. Generally, IEEE Std. 802 prescribes the functional, electrical and mechanical protocols, and the physical and data link layers for Local and Metropolitan Area Networks (LAN/MAN). The specification augments network principles, conforming to the ISO seven-layer model for OSI, commonly referred to as "Ethernet". In the hierarchy of the seven-layer model, the lowest layers, the so-called physical and data link layers, comprise functional modules that specify the physical transmission media and the way network nodes interface to it, the mechanics of transmitting information over the media in an error-free manner, and the format the information must take in order to be transmitted.
While there are several LAN technologies in use today, Ethernet is by far the most popular. The Ethernet standards include protocols for a 10 Mbps baseband transmissions typically referred to as 10Base-X. Computers equipped with a 10Base-X Ethernet interface attachments may link to other computers over an Ethernet LAN. These Ethernet LAN's provide fast and reliable data transmission networks. Nevertheless, the need for faster data transmission has led to the development of faster standards. One such standard includes the Fast Ethernet standards typically referred to as 100Base-X. The 100Base-X standards generally follow the 10Base-X standards except that the baseband data transmission rate increases from 10 Mbps to 100 Mbps. The 100Base-X standard, however, retains the original CSMA/CD medium access control mechanism.
The 100Base-X standards include the 100Base-T standard for interconnecting devices over an ordinary twisted pair telephone cable. The 100Base-T standard is popular for providing an inexpensive LAN in many modern offices.
In March 1995 an IEEE 802.3 task force was formed for developing transceiver specification on an IEEE 802.3 100Base-T2 media type. On Mar. 5, 1996 a preliminary IEEE draft was published identifying changes to IEEE standard 802.3 100Base-T designated IEEE standard P802.3y, herein incorporated by reference. The standard specifies the family of physical layer implementations including one for 100Base-T2 which uses two pairs of ISO/IEC 11801 category 3, 4, or 5 balance cable.
10Base-T and 100Base-Tx are already widely established within the networking industry, while 100Base-T2 is an emerging standard. Other technology standards are also available or emerging such as 100 Base T4 or 1 Gigabit standards. Physical Layer devices may contain multiple technology transceivers to support 10 Base T, 100 Base X, 100 Base T4, or 1 Gigabit technologies, including auto-negotiation functions.
The IEEE Standard 802.3 100Base-T Fast Ethernet and draft changes to IEEE 802.3 100Base-T include mechanisms for auto-negotiation of the media speed. As the 100 Mbps standard becomes more widely adopted, computers are being equipped with Ethernet interfaces that operate at both 10 Mbps and 100 Mbps. The auto-negotiation function is an optional part of the Ethernet standard that allows the devices to exchange information about their abilities. This, in turn, allows the devices to perform automatic configuration to select a common communication mode over the link. Generally, auto-negotiation provides automatic speed matching for multi-speed devices on a LAN. Multi-speed Ethernet interfaces can then take advantage of the highest speed offered on the LAN.
After establishing an Ethernet connection, network devices typically transmit encoded baseband serial data. The devices package the data into frames sometimes referred to as a packet. Each Ethernet packet typically includes a preamble (62 bits long), a start of frame delimiter (2 bits long), a destination address (6 bytes long), a source address (6 bytes long), a type field address (2 bytes long), a data field (46 to 1.5K bytes long), and a frame check sequence (4 bytes long). These packets are physically sent over a network which interconnects devices.
The basic mechanism to achieve auto-negotiation is to pass information encapsulated within a burst of closely spaced linked tertiary test pulses that individually meet the 10Base-T transmitter waveform for linked test pulse. This burst of pulses is referred to as a fast link pulse (FLP) burst. The FLP burst consists of a series of link and tertiary test pulses that form an alternating clock/data sequence. Extraction of the data bits from the FLP burst yields a Link Code Word that identifies the operational mode supported by the remote device, as well as some information used for the auto-negotiation function's handshake mechanism. Multiple technologies may be advertised via the Link Code Word, and each device must support the data service ability for a technology it advertises.
The auto-negotiation arbitration function is responsible for determining the common mode of operation shared by link partners and for resolving multiple common modes. Since two devices may have multiple abilities in common, IEEE 802.3u and P802.3y specify a prioritization scheme to insure that the highest common denominator ability is chosen.
To enable the autonegotiation functions, a Physical layer device will contain an autonegotiation state machine. The autonegotiation state machine will first check to see if autonegotiation is enabled after reset. If autonegotiation is not enabled, the state machine remains in this state. If autonegotiation is enabled, the state machine disables transmission, waits for a period of time guaranteed to break the link with the connected partner, and then begins the autonegotiation process as described above. As mentioned, once the link is broken, the local device transmits Fast Link Pulses which announce its available technologies to the connected device. The local device also waits for either fast link pulses or signals characteristic of a specific technology to be transmitted by the connected device.
This second method is known as parallel detection. However, parallel detection causes a problem in Physical Layer Devices implementing multiple technologies and/or multiple ports. Receivers for each technology must be enabled on each port causing power consumption that requires more expensive IC packages and heat dissipation techniques.
Thus, it can be seen that there is a need to decrease the power required by the receivers during parallel detection.
It can also be seen that there is a need for the receivers to be enabled for a brief period of time to check for the presence of the required signals, and then be disabled for a much greater period of time before being enabled again.
It can also be seen that there is a need for Physical Layer Devices containing multiple ports that can stagger the enabling of the receivers so that only one port's receiver is active at any given time.